Watershed hydrology and salinity, but not nutrient chemistry, are associated with arid-land stream microbial diversity

AbstractMicrobiota in streams drive many ecosystem functions, including whole-stream metabolism, nitrogen (N) cycling, and the production of basal resources that fuel stream food webs. Interactions between surface water and shallow, subsurface groundwater produce the oxygen and nutrient gradients that influence these microbially mediated biogeochemical functions. Microbial nutrient processing is often limited by nutrient availability, but we lack a clear understanding of the relationships between hydrology, water chemistry, microbial composition, and nutrient cycling. In this study we evaluated the prediction that the microbial (bacterial and archaeal) assemblage composition in surface and subsurface water (both within and among stream reaches) would be related to dissolved nutrient concentrations, surface–subsurface hydrologic connectivity, and reach-scale N cycling rates. To evaluate our predictions, we collected data on water chemistry, whole-stream hydrological connectivity, biogeochemical function, a...